[en] We report on a study of the magnetic structure and phase transitions of the UAs_1-xSe_x solid solutions employing x-ray and neutron scattering. We have focused this study on compositions 0.18< x<0.22, in which magnetic structures having double-k and triple-k configurations are found with increasing x. In general, our findings are in excellent agreement with those reported by Kuznietz using solely neutron diffraction. However, our x-ray studies have added several important details about (1) the incommensurate transitions near T_N, (2) the nature of the 2k-3k phase boundary, and (3) the discovery of a new magnetic phase

[en] Magnetic Resonance Imaging (MRI) offers the best textbook example for the exploitation of both Heike Kamerlingh Onnes's major discoveries, namely the liquefaction of liquid helium and superconductivity. This paper will briefly describe how MRI images are acquired, give a historical account about the early days, and then focus on the magnet. It provides a window into the world of physics and engineering of magnet technology and it will chart the magnet design evolution since inception. For example, over the past 20 years, magnet designers have taken 1.5T MRI magnets from a weight of 13tonnes and a length of 2.40m in 1989 to a weight of 3.2tonnes and a length of 1.37m in 2009. The 3T products have also undergone similar developments. Coils experience mechanical forces of order 380tonnes. The cryogenics for MRI magnets have also undergone major improvements. Today's magnets do not use liquid nitrogen and most importantly have zero helium loss, thus needing no refill. Combined with the weight, this makes the body scanner accessible to developing countries and easy to site in any room. Although the future may eliminate the need for liquid helium completely, MRI will always continue to depend on superconductivity.

[en] The phase transition at T₀ = 25 K in NpO₂ and the single-ion nature of the Np 5f electrons is examined in the light of the results of resonant x-ray scattering experiments at the M₄ Np edge. These experiments exclude usual magnetic dipole ordering at T₀, and provide direct evidence of long-range order of the electric quadrupole moment with Γ₅ symmetry. The phase transition is purely electronic and does not involve either internal or external crystallographic distortions, so the symmetry of the system remains cubic. The primary order parameter (OP) is associated with Γ₄^t magnetic octupoles, ordering in a triple-q longitudinal structure defined by the three wavevectors of the (001) star. Magnetic octupolar order breaks invariance under time reversal and induces the order of electric quadrupoles as the secondary OP. The resulting ground state is a singlet with zero dipole magnetic moment

[en] An asymmetric shift in the position of the magnetic Bragg peak with respect to the fiducial lattice has been observed by resonant x-ray scattering in a diverse series of antiferromagnetic compounds. A possible explanation is given in terms of a generalized Berry phase correction